Overdoping effect on pair breaking peak energy in the electronic Raman spectra of high-Tc cuprate superconductors

Abstract

In the superconducting state of cuprates we have measured electronic Raman spectra (ERS) and plotted the pair breaking energy as a function of hole concentration in overdoped regime. The target materials in this study are Ca-substituted YBCO and Tl2201, both of which have similar Tc when it is optimally doped but different number of CuO2 planes in the unit cell. For both materials pair breaking peak energy (Eb) shows decrease with increasing carrier concentration. Interestingly Eb seems to show a rapid drop at a certain carrier concentration, where several measurements suggest the signature of quantum critical point. The similarity of the ERS between the two materials indicates that the behavior is not affected by the number of CuO2 planes in a unit cell, and that electronic state of cuprates may have a remarkable change at the critical hole concentration.